Minimizing the threat of pandemic emergence from avian influenza in poultry systems

Abstract

BackgroundLive-animal markets are a culturally important feature of meat distribution chains in many populations, yet they provide an opportunity for the maintenance and transmission of potentially emergent zoonotic pathogens. The ongoing human outbreak of avian H7N9 in China highlights the need for increased surveillance and control in these live-bird markets (LBMs).DiscussionClosure of retail markets in affected areas rapidly decreased human cases to rare, sporadic occurrence, but little attention has been paid thus far to the role of upstream elements of the poultry distribution chain such as wholesale markets. This could partly explain why transmission in poultry populations has not been eliminated more broadly. We present surveillance data from both wholesale live-bird markets (wLBMs) and rLBMs in Shantou, China (from 2004–2006), and call on disease-dynamic theory to illustrate why closing rLBMs has only minor effects on the overall volume of transmission. We show that the length of time birds stay in rLBMs can severely limit transmission there, but that the system-wide effect may be reduced substantially by high levels of transmission upstream of retail markets.SummaryManagement plans that minimize transmission throughout the entire poultry supply chain are essential for minimizing exposure to the public. These include reducing stay-time of birds in markets to 1 day, standardizing poultry supply chains to limit transmission in pre-retail settings, and monitoring strains with epidemiological traits that pose a high risk of emergence. These actions will further limit human exposure to extant viruses and reduce the likelihood of the emergence of novel strains by decreasing the overall volume of transmission.

The role of live poultry movement and live bird market biosecurity in the epidemiology of influenza A (H7N9): A cross-sectional observational study in four eastern China provinces

“…18 Other studies have shown that the prevalence of particular avian influenza viruses in retail LBMs is twice as high as the prevalence in wholesale LBMs. 26,27 However, our results have shown that in the case of H7N9, the market level infection was significantly associated with wholesale and mixed LBMs compared to retail markets suggesting that particular biosecurity practices within wholesale and mixed LBMs may be a good indicator for H7N9 presence. Initial reports had proposed that visits to retail markets during the first wave of H7N9 had posed humans at increased risk of H7N9 infection by facilitating the transmission of avian influenza viruses due to lower biosecurity levels and increased access by consumers.…”

Interventions to reduce zoonotic and pandemic risks from avian influenza in Asia

“…37 A major reason for the effectiveness of this intervention is that incoming chicken are not in the market for long enough to be newly infected, shed virus and infect others as simulated in mathematical models. 38 The emptying of the market of live poultry overnight deprives the virus of a permissive host for replication. Disinfection and cleaning of markets while live poultry remain within them is unlikely have this impact.…”

“…While it is clearly not possible to prevent the mingling of ducks from chickens in rural backyard settings, this is probably not as important as the large-scale intermingling and genetic reassortment of viruses that takes place within the wholesale and retail poultry marketing systems in China and other parts of Asia. 38 Re-engineering these poultry marketing systems to separate aquatic from terrestrial poultry in the longer term is sustainable and not beyond the realms of feasibility in Asia. Such an intervention was introduced in Hong Kong SAR following the initial H5N1 outbreak in 1997 and continues to date, with aquatic poultry (ducks, geese) being centrally slaughtered though terrestrial poultry continued to be sold in retail LPM.…”

Emerging viral respiratory tract infections—environmental risk factors and transmission

“…93,94 Signs and symptoms are consistent with other infl uenzalike illnesses and include chills, 93,94 cough, chest pain, shivering, pneumonia, respiratory failure, acute respiratory distress syndrome, and multiorgan failure. 79,82,94 Despite the few human cases, 92 these H10N8 infections are a cause for concern because this is the fi rst H10N8 infl uenza virus to aff ect human beings. 95…”